The invention is directed to purified and isolated TNF-xcex1 converting enzyme, the nucleic acids encoding such enzyme, processes for production of recombinant TNF-xcex1 convertases, pharmaceutical compositions containing such enzymes, and their use in various assays and therapies.
Tumor necrosis factor-xcex1 (TNF-xcex1, also known as cachectin) is a mammalian protein capable of inducing a variety of effects on numerous cell types. TNF-xcex1 was initially characterized by its ability to cause lysis of tumor cells and is produced by activated cells such as mononuclear phagocytes;T-cells, B-cells, mast cells and NK cells. There are two forms of TNF-xcex1, a type II membrane protein of relative molecular mass 26,000 (26 kD) and a soluble 17 kD form generated from the cell-bound protein by proteolytic cleavage. TNF-xcex1 is a principal mediator of the host response to gram-negative bacteria. Lipopolysaccharide (LPS, also called endotoxin), derived from the cell wall of gram-negative bacteria, is a potent stimulator of TNF-xcex1 synthesis. Because the deleterious effects which can result from an over-production or an unregulated-production of TNF-xcex1 are extremely serious, considerable efforts have been made to control or regulate the serum level of TNF-xcex1. An important part in the effort to effectively control serum TNF-xcex1 levels is the understanding of the mechanism of TNF-xcex1 biosynthesis.
The mechanism by which TNF-xcex1 is secreted has not previously been elucidated. Kriegler et al. Cell, 53:45 (1988) conjectured that TNF-xcex1 xe2x80x9csecretionxe2x80x9d is due to the converting of the 26 k membrane-bound molecule by a then unknown proteolytic enzyme or protease. Scuderi et. al., J. Immunology, 143:168 (1989), suggested that the release of TNF-xcex1 from human leukocyte cells is dependent on one or more serine proteases, e.g., a leukocyte elastase or trypsin. A serine protease inhibitor, p-toluenesulfonyl-L-arginine methyl ester, was found to suppress human leukocyte TNF-xcex1 release in a concentration-dependent manner. Scuderi et. al. suggested that an arginine methyl ester competes for the arginine-binding site in the enzyme""s reactive center and thereby blocks hydrolysis. The lysine and phenylalanine analogs of the inhibitor reportedly failed to mimic the arginine methyl ester. However, it was never shown that this compound acted by inhibiting a protease that cleaves the 26 kD TNF. More recently, it has been reported that metalloprotease inhibitors block the release of TNF from THP-1 cells. See Mohler et al., Nature 370:218 (1994); Gearing et al., Nature, 370:555 (1994); and McGeehan et al., Nature, 370:568 (1994).
Most, but not all, proteases recognize a specific amino acid sequence. Some proteases primarily recognize residues located N-terminal of the cleaved bond, some recognize residues located C-terminal of the cleaved bond, and some proteases recognize residues on both sides of the cleaved bond. Metalloprotease enzymes utilize a bound metal ion, generally Zn2+, to catalyze the hydrolysis of the peptide bond. Metalloproteases are implicated in joint destruction (the matrx metalloproteases), blood pressure regulation (angiotensin converting enzyme), and regulation of peptide-hormone levels (neutral endopeptidase-24.11).
The invention pertains to biologically active TNF-xcex1 converting enzyme (xe2x80x9cTACExe2x80x9d) as an isolated and purified polypeptide. In addition, the invention is directed to isolated nucleic acids encoding TACE and to expression vectors comprising a cDNA encoding TACE. Within the scope of this invention are host cells that have been transfected or transformed with expression vectors that comprise a cDNA encoding TACE, and processes for producing TACE by culturing such host cells under conditions conducive to expression of TACE. By virtue of the purification of TACE, antibodies, and in particular, monoclonal antibodies against TACE are an aspect of the invention. In addition, assays utilizing TACE to screen for potential inhibitors thereof, and methods of using TACE as a therapeutic agent for the treatment of diseases mediated by cell-bound TNF-xcex1 or other molecules are encompassed by the invention. Further, methods of using TACE in the design of inhibitors thereof are also an aspect of the invention.
The isolated and purified metalloprotease of the invention is capable of converting TNF-xcex1 from the 26 kD membrane-bound form to the 17 kD form, and which has a molecular weight of between approximately 66 kD and approximately 97 kD. The cDNA sequence of TACE is shown in SEQ ID NO:1. The isolated and purified TNF-xcex1 converting enzyme (xe2x80x9cTACExe2x80x9d) comprises amino acids 18-824 of SEQ ID NO:2.
Inhibition of the TACE inhibits release of TNf-xcex1 into the serum and other extracellular spaces. TACE inhibitors would therefore have clinical utility in treating conditions characterized by over-production or upregulated production of TNF-xcex1. A particularly useful TACE inhibitor for certain pathological conditions would selectively inhibit TACE while not affecting TNF-xcex2 (also known as lymphotoxin) serum levels. The over-production or unregulated production of TNF-xcex1 has been implicated in certain conditions and diseases, for example, Systemic Inflammatory Response Syndrome, reperfusion injury, cardiovascular disease, infectious disease such as HIV infection and HIV neuropathy, obstetrical or gynecological disorders, inflammatory disease/auto-immunity, allergic/atopic diseases, malignancy, transplants including organ transplant rejection or graft-versus-host disease, cachexia, congenital, dermatologic, neurologic, renal, toxicity, and metabolic/idiopathic diseases.
Inhibitors of TACE would prevent the cleavage of cell-bound TNF-xcex1 thereby reducing the level of TNF-xcex1 in serum and tissues. The present invention encompasses such an embodiment and comprises a method of inhibiting the cleavage of TNF-xcex1 from cell membranes in a mammal comprising administering to such mamma an effective amount of a compound that inhibits the TNF-xcex1 proteolytic activity of an enzyme comprising the sequence of amino acids from 18 to 671 through 824 of SEQ ID NO:2. In addition, the invention comprises a method for treating a mammal having a disease characterized by an overproduction or an upregulated production of TNF-xcex1, comprising administering to the mammal a composition comprising an effective amount of a compound that inhibits the TNF-xcex1 proteolytic activity of an enzyme comprising the sequence of amino acids 18-824 of SEQ ID NO:2. Such inhibitors would be of significant clinical utility and could be potential therapeutics for treating the above-listed TNF-xcex1-related disorders. Isolation and purification of TACE would provide a significant advancement in the effort to develop inhibitors of such enzyme, and the treatment of TNF-associated diseases, and indeed, could lead to use of TACE itself as a therapeutic agent for certain physiological disorders. For example, in addition to TNF-xcex1, other cytokines as well as cytokine receptors and several adhesion proteins may be released from the cell surface by TACE or related proteases. TACE may be administered to modulate or remove cell surface cytokines, cytokine receptors and adhesion proteins involved in tumor cell growth, inflammation, or fertilization.
A cDNA encoding human TNF-xcex1 converting enzyme (xe2x80x9cTACExe2x80x9d) has been isolated and is disclosed in SEQ ID NO:1. This discovery of the cDNA encoding human TACE enables construction of expression vectors comprising nucleic acid sequences encoding TACE; host cells transfected or transformed with the expression vectors; biologically active human TACE as isolated and purified proteins; and antibodies imnmunoreactive with TACE.
Isolated and purified TACE polypeptides according to the invention are useful for detecting the TACE-inhibiting activity of a molecule. In such a method involving routine and conventional techniques, a molecule of unknown TACE-inhibiting activity is mixed with a substrate and incubated with a TACE polypeptide. The extent of substrate cleavage then can be determined chromatographically.
In addition, TACE polypeptides according to the invention are useful for the structure-based design of a TACE inhibitor. Such a design would comprise the steps of determining the three-dimensional structure of such TACE polypeptide, analyzing the three-dimensional structure for the likely binding sites of substrates, synthesizing a molecule that incorporates a predictive reactive site, and determining the TACE-inhibiting activity of the molecule.
Antibodies immunoreactive with TACE, and in particular, monoclonal antibodies against TACE, are now made available through the invention. Such antibodies may be useful for inhibiting TACE activity in vivo and for detecting the presence of TACE in a sample.
As used herein, the term xe2x80x9cTACExe2x80x9d refers to a genus of polypeptides that are capable of converting the 26 kD cell membrane-bound form of TNF-xcex1 (that includes an intracellular region, a membrane region, and an extracellular region), into the soluble 17 kD form that comprises the C-terminal 156 residues of the TNF-xcex1 protein. TACE encompasses proteins having the amino acid sequence 18 to 824 of SEQ ID NO:2, as well as those proteins having a high degree of similarity (at least 80%, and more preferably 90% homology) with the amino acid sequence 18 to 824 of SEQ ID NO:2 and which proteins are biologically active. In addition, TACE refers to the biologically active gene products of the nucleotides 52-2472 of SEQ ID NO:1. Further encompassed by the term xe2x80x9cTACExe2x80x9d are the membrane-bound proteins (which include an intracellular region, a membrane region, and an extracellular region), and soluble or truncated proteins which comprise primarily the extracellular portion of the protein, retain biological activity and are capable of being secreted. Specific examples of such soluble proteins are those comprising the sequence of amino acids 18-671 of SEQ ID NO:2. Truncated versions are those having less than the extracellular portion of the protein and comprise, for example, amino acids 18-477 of SEQ ID NO:2, or that comprise substantially all of the catalytic domain, i.e., amino acids 215 to 477 of SEQ ID NO:2.
The isolated and purified TACE according to the invention has a molecular weight between about 66 kD and about 97 kD as determined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). More specifically, TACE was found to have a molecular weight of approximately 80 kD as determined by SDS-PAGE.
The term xe2x80x9cisolated and purifiedxe2x80x9d as used herein, means that TACE is essentially free of association with other proteins or polypeptides, for example, as a purification product of recombinant host cell culture or as a purified product from a non-recombinant source. The term xe2x80x9csubstantially purifiedxe2x80x9d as used herein, refers to a mixture that contains TACE and is essentially free of association with other proteins or polypeptides, but for the presence of known proteins that can be removed using a specific antibody, and which substantially purified TACE retains biological activity. The term xe2x80x9cpurified TACExe2x80x9d refers to either the xe2x80x9cisolated and purifiedxe2x80x9d form of TACE or the xe2x80x9csubstantially purifiedxe2x80x9d form of TACE, as both are described herein.
The term xe2x80x9cbiologically activexe2x80x9d as it refers to TACE, means that the TACE is capable of converting the 26 kD cell form of TNF-xcex1 into the 17 cD form.
A xe2x80x9cnucleotide sequencexe2x80x9d refers to a polynucleotide molecule in the form of a separate fragment or as a component of a larger nucleic acid construct, that has been derived from DNA or RNA isolated at least once in substantially pure form (i.e., free of contaminating endogenous materials) and in a quantity or concentration enabling identification, manipulation, and recovery of its component nucleotide sequences by standard biochemical methods (such as those outlined in Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratiry, Cold Spring Harbor, N.Y. (1989)). Such sequences are preferably provided in the form of an open reading frame uninterrupted by internal non-translated sequences, or introns, that are typically present in eukaryotic genes. Sequences of non-translated DNA may be present 5xe2x80x2 or 3xe2x80x2 from an open reading frame, where the same do not interfere with manipulation or expression of the coding region.
A xe2x80x9cTACE variantxe2x80x9d as referred to herein, means a polypeptide substantially homologous to native TACE, but which has an amino acid sequence different from that of native TACE (human, murine or other mammalian species) because of one or more deletions, insertions or substitutions. The variant amino acid sequence preferably is at least 80% identical to a native TACE amino acid sequence, most preferably at least 90% identical. The percent identity may be determined, for example, by comparing sequence information using the GAP computer program, version 6.0 described by Devereux et al. (Nucl. Acids Res. 12:387, 1984) and available from the University of Wisconsin Genetics Computer Group (UWGCG). The GAP program utilizes the alignment method of Needleman and Wunsch (J. Mol. Biol. 48:443, 1970), as revised by Smith and Waterman (Adv. Appl. Math 2:482, 1981). The preferred default parameters for the GAP program include: (1) a unary comparison matrix (containing a value of 1 for identities and 0 for non-identities) for nucleotides, and the weighted comparison matrix of Gribskov and Burgess, Nucl. Acids Res. 14:6745, 1986, as described by Schwartz and Dayhoff, eds., Atlas of Protein Sequence and Structure, National Biomedical Research Foundation, pp. 353-358, 1979; (2) a penalty of 3.0 for each gap and an additional 0.10 penalty for each symbol in each gap; and (3) no penalty for end gaps.
Variants may comprise conservatively substituted sequences, meaning that a given amino acid residue is replaced by a residue having similar physiochemical characteristics. Conservative substitutions are well known in the art and include substitution of one aliphatic residue for another, such as Ile, Val, Leu, or Ala for one another, or substitutions of one polar residue for another, such as between Lys and Arg, Glu and Asp; or Gln and Asn. Conventional procedures and methods can be used for making and using such variants. Other such conservative substitutions, for example, substitutions of entire regions having similar hydrophobicity characteristics, are well known and routinely performed. Naturally occurring TACE variants are also encompassed by the invention. Examples of such variants are proteins that result from alternate mRNA splicing events or from proteolytic cleavage of the TACE protein, wherein the TACE proteolytic property is retained. Alternate splicing of mRNA may yield a truncated but biologically active TACE protein, such as a naturally occurring soluble form of the protein, for example, as shown in SEQ ID NO:4. Variations attributable to proteolysis include, for example, differences in the N- or C-termini upon expression in different types of host cells, due to proteolytic removal of one or more terminal amino acids from the TACE protein (generally from 1-5 terminal amino acids).
As stated above, the invention provides isolated and purified, or homogeneous, TACE polypeptides, both recombinant and non-recombinant. Variants and derivatives of native TACE proteins that retain the desired biological activity may be obtained by mutations of nucleotide sequences coding for native TACE polypeptides. Alterations of the native amino acid sequence may be accomplished by any of a number of conventional methods. Mutations can be introduced at particular loci by synthesizing oligonucleotides containing a mutant sequence, flanked by restriction sites enabling ligation to fragments of the native sequence. Following ligation, the resulting reconstructed sequence encodes an analog having the desired amino acid insertion, substitution, or deletion.
Alternatively, oligonucleotide-directed site-specific mutagenesis procedures can be employed to provide an altered gene wherein predetermined codons can be altered by substitution, deletion or insertion. Exemplary methods of making the alterations set forth above are disclosed by Walder et al. (Gene 42:133, 1986); Bauer et al. (Gene 37:73, 1985); Craik (BioTechniques, Jan. 12-19, 1985); Smith et al. (Genetic Engineering: Principles and Methods, Plenum Press, 1981); Kunkel (Proc. Natl. Acad. Sci. USA 82:488, 1985); Kunkel et al. (Methods in Enzymol. 154:367, 1987); and U.S. Pat. Nos. 4,518,584 and 4,737,462 all of which are incorporated by reference.
TACE may be modified to ceate TACE derivatives by forming covalent or aggregative conjugates with other chemical moieties, such as glycosyl groups, polyethylene glycol (PEG) groups, lipids, phosphate, acetyl groups and the like. Covalent derivatives of TACE may be prepared by linking the chemical moieties to functional groups on TACE amino acid side chains or at the N-terminus or C-terminus of a TACE polypeptde or the extracellular domain thereof. Other derivatives of TACE within the scope of this invention include covalent or aggregative conjugates of TACE or its fragments with other proteins or polypeptides, such as by synthesis in recombinant culture as N-termninal or C-terminal fusions. For example, the conjugate may comprise a signal or leader polypeptide sequence (e.g. the xcex1-factor leader of Saccharomyces) at the N-terminus of a TACE polypeptide. The signal or leader peptide co-translationally or post-translationally directs transfer of the conjugate from its site of synthesis to a site inside or outside of the cell membrane or cell wall.
TACE polypeptide conjugates can comprise peptides added to facilitate purification and identification of TACE. Such peptides include, for example, poly-His or the antigenic identification peptides described in U.S. Pat. No. 5,011,912 and in Hopp et al., Bio/Technology 6:1204, 1988.
The invention further includes TACE polypeptides with or without associated native-pattern glycosylation. TACE expressed in yeast or mammalian expression systems (e.g., COS-7 cells) may be similar to or significantly different from a native TACE polypeptide in molecular weight and glycosylation pattern, depending upon the choice of expression system. Expression of TACE polypeptides in bacterial expression systems, such as E. coli, provides non-glycosylated molecules. Glycosyl groups may be removed through conventional methods, in particular those utilizing glycopeptidase. In general, glycosylated TACE may be incubated with a molar excess of glycopeptidase (Boehringer Mannheim).
Equivalent DNA constructs that encode various additions or substitutions of amino acid residues or sequences, or deletions of terminal or internal residues or sequences not needed for biological activity are encompassed by the invention. For example, N-glycosylation sites in the TACE extracellular domain can be modified to preclude glycosylation, allowing expression of a reduced carbohydrate analog in mammalian and yeast expression systems. N-glycosylation sites in eukaryotic polypeptides are characterized by an amino acid triplet Asn-X-Y, wherein X is any amino acid except Pro and Y is Ser or Thr. Appropriate substitutions, additions or deletions to the nucleotide sequence encoding these triplets will result in prevention of attachment of carbohydrate residues at the Asn side chain. Alteration of a single nucleotide, chosen so that Asn is replaced by a different amino acid, for example, is sufficient to inactivate an N-glycosylation site. Known procedures for inactivating N-glycosylation sites in proteins include those described in U.S. Pat. No. 5,071,972 and EP 276,846, hereby incorporated by reference.
In another example, sequences encoding Cys residues that are not essential for biological activity can be altered to cause the Cys residues to be deleted or replaced with other amino acids, preventing formation of incorrect intramolecular disulfide bridges upon renaturation. Other equivalents are prepared by modification of adjacent dibasic amino acid residues to enhance expression in yeast systems in which KEX2 protease activity is present. EP 212,914 discloses the use of site-specific mutagenesis to inactivate KEX2 protease processing sites in a protein. KEX2 protease processing sites are inactivated by deleting, adding or substituting residues to alter Arg-Arg, Arg-Lys, and Lys-Arg pairs to eliminate the occurrence of these adjacent basic residues. Lys-Lys pairings are considerably less susceptible to KEX2 cleavage, and conversion of Arg-Lys or Lys-Arg to Lys-Lys represents a conservative and preferred approach to inactivating KEX2 sites.
Nucleic acid sequences within the scope of the invention include isolated DNA and RNA sequences that hybridize to the native TACE nucleotide sequences disclosed herein under conditions of moderate or high stringency, and which encode biologically active TACE. Conditions of moderate stringency, as known to those having ordinary skill in the art, and as defined by Sambrook et al. Molecular Cloning: A Laboratory Manual, 2 ed. Vol. 1, pp. 1.101-104, Cold Spring Harbor Laboratory Press, (1989), include use of a prewashing solution of 5X SSC, 0.5% SDS, 1.0 mM EDTA (pH 8.0) and hybridization conditions of about 50xc2x0 C.-60xc2x0 C., 5 X SSC, overnight, preferably 55xc2x0 C. Conditions of high stringency include higher temperatures of hybridization and washing. The skilled artisan will recognize that the temperature and wash solution salt concentration may be adjusted as necessary according to factors such as the length of the probe.
Due to the known degeneracy of the genetic code wherein more than one codon can encode the same amino acid, a DNA sequence may vary from that shown in SEQ ID NO:1 and still encode a TACE protein having the amino acid sequence of SEQ ID NO:2. Such variant DNA sequences may result from silent mutations (e.g., occurring during PCR amplification), or may be the product of deliberate mutagenesis of a native sequence.
The invention thus provides equivalent isolated DNA sequences encoding biologically active TACE, selected from: (a) the coding region of a native mammalian TACE gene; (b) cDNA comprising the nucleotide sequence presented in SEQ ID NO:1; (c) DNA capable of hybridization to a DNA of (a) under moderately stringent conditions and which encodes biologically active TACE; and (d) DNA which is degenerate as a result of the genetic code to a DNA defined in (a), (b) or (c) and which encodes biologically active TACE. TACE proteins encoded by such DNA equivalent sequences are encompassed by the invention.
DNA that are equivalents to the DNA sequence of SEQ ID NO:1 will hybridize under moderately stringent or highly stringent conditions to the double-stranded native DNA sequence that encode polypeptides comprising amino acid sequences of 18-Xaa of SEQ ID NO:2, wherein Xaa is an amino acid from 671 to 824. Examples of TACE proteins encoded by such DNA, include, but are not limited to, TACE fragments (soluble or membrane-bound) and TACE proteins comprising inactivated N-glycosylation site(s), inactivated KEX-2 protease processing site(s), or conservative amino acid substitution(s), as described above. TACE proteins encoded by DNA derived from other mammalian species, wherein the DNA will hybridize under conditions of moderate or high stringency to the complement of the cDNA of SEQ ID NO:1 are also encompassed.
Alternatively, TACE-binding proteins, such as the anti-TACE antibodies of the invention, can be bound to a solid phase such as a column chromatography matrix or a similar substrate suitable for identifying, separating or purifying cells that express the TACE on their surface. Adherence of TACE-binding proteins to a solid phase contacting surface can be accomplished by any means, for example, magnetic microspheres can be coated with TACE-binding proteins and held in the incubation vessel through a magnetic field. Suspensions of cell mixtures are contacted with the solid phase that has TACE-binding proteins thereon. Cells having TACE on their surface bind to the fixed TACE-binding protein and unbound cells then are washed away. This affinity-binding method is useful for purifying, screening or separating such TACE-expressing cells from solution. Methods of releasing positively selected cells from the solid phase are known in the art and encompass, for example, the use of enzymes. Such enzymes are preferably non-toxic and non-injurious to the cells and are preferably directed to cleaving the cell-surface binding partner.
Alternatively, mixtures of cells suspected of containing TACE-expressing cells first can be incubated with a biotinylated TACE-binding protein. Incubation periods are typically at least one hour in duration to ensure sufficient binding to TACE. The resulting mixture then is passed through a column packed with avidin-coated beads, whereby the high affinity of biotin for avidin provides the binding of the TACE-binding cells to the beads. Use of avidin-coated beads is known in the art. See Berenson, et al. J. Cell. Biochem., 10D:239 (1986). Wash of unbound material and the release of the bound cells is performed using conventional methods.
In the methods described above, suitable TACE-binding proteins are anti-TACE antibodies, and other proteins that are capable of high-affinity binding of TACE. A preferred TACE-binding protein is an anti-TACE monoclonal antibody obtained, for example, as described in Example 4.
TACE polypeptides may exist as oligomers, such as covalently-linked or non-covalently-linked dimers or trimers. Oligomers may be linked by disulfide bonds formed between cysteine residues on different TACE polypeptides. In one embodiment of the invention, a TACE dimer is created by fusing TACE to the Fc region of an antibody (e.g., IgG1) in a manner that does not interfere with biological activity of TACE. The Fc polypeptide preferably is fused to the C-terminus of a soluble TACE (comprising only the extracellular domain). General preparation of fusion proteins comprising heterologous polypeptides fused to various portions of antibody-derived polypeptides (including the Fe domain) has been described, e.g., by Ashkenazi et al. (PNAS USA 88:10535, 1991) and Byrn et al. (Nature 344:677, 1990), hereby incorporated by reference. A gene fusion encoding the TACE:Fc fusion protein is inserted into an appropriate expression vector. TACE:Fc fusion proteins are allowed to assemble much like antibody molecules, whereupon interchain disulfide bonds form between Fc polypeptides, yielding divalent TACE. If fusion proteins are made with both heavy and light chains of an antibody, it is possible to form a TACE oligomer with as many as four TACE extracellular regions. Alternatively, one can link two soluble TACE domains with a peptide linker.
Recombinant expression vectors containing a nucleic acid sequence encoding TACE can be prepared using well known methods. The expression vectors include a TACE DNA sequence operably linked to suitable transcriptional or translational regulatory nucleotide sequences, such as those derived from a mammalian, microbial, viral, or insect gene. Examples of regulatory sequences include transcriptional promoters, operators, or enhancers, an mRNA ribosomal binding site, and appropriate sequences which control transcription and translation initiation and termination. Nucleotide sequences are xe2x80x9coperably linkedxe2x80x9d when the regulatory sequence functionally relates to the TACE DNA sequence. Thus, a promoter nucleotide sequence is operably linked to a TACE DNA sequence if the promoter nucleotide sequence controls the transcription of the TACE DNA sequence. The ability to replicate in the desired host cells, usually conferred by an origin of replication, and a selection gene by which transformants are identified, may additionally be incorporated into the expression vector.
In addition, sequences encoding appropriate signal peptides that are not naturally associated with TACE can be incorporated into expression vectors. For example, a DNA sequence for a signal peptide (secretory leader) may be fused in-frame to the TACE sequence so that TACE is initially translated as a fusion protein comprising the signal peptide. A signal peptide that is functional in the intended host cells enhances extracellular secretion of the TACE polypeptide. The signal peptide may be cleaved from the TACE polypeptide upon secretion of TACE from the cell.
Suitable host cells for expression of TACE polypeptides include prokaryotes, yeast or higher eukaryotic cells. Appropriate cloning and expression vectors for use with bacterial, fungal, yeast, and mammalian cellular hosts are described, for example, in Pouwels et al. Cloning Vectors: A Laboratory Manual, Elsevier, N.Y., (1985). Cell-free translation systems could also be employed to produce TACE polypeptides using RNAs derived from DNA constructs disclosed herein.
Prokaryotes include gram negative or gram positive organisms, for example, E. coli or Bacilli. Suitable prokaryotic host cells for transformation include, for example, E. coli, Bacillus subtilis, Salmonella typhimurium, and various other species within the genera Pseudomonas, Streptomyces, and Staphylococcus. In a prokaryotic host cell, such as E. coli, a TACE polypeptide may include an N-terminal methionine residue to facilitate expression of the recombinant polypeptide in the prokaryotic host cell. The N-terminal Met may be cleaved from the expressed recombinant TACE polypeptide.
Expression vectors for use in prokaryotic host cells generally comprise one or more phenotypic selectable marker genes. A phenotypic selectable marker gene is, for example, a gene encoding a protein that confers antibiotic resistance or that supplies an autotrophic requirement. Examples of useful expression vectors for prokaryotic host cells include those derived from commercially available plasmids such as the cloning vector pBR322 (ATCC 37017). pBR322 contains genes for ampicillin and tetracycline resistance and thus provides simple means for identifying transformed cells. To construct en expression vector using pBR322, an appropriate promoter and a TACE DNA sequence are inserted into the pBR322 vector. Other commercially available vectors include, for example, pKK223-3 (Pharmacia Fine Chemicals, Uppsala, Sweden) and pGEM1 (Promega Biotec, Madison, Wis., USA).
Promoter sequences commonly used for recombinant prokaryotic host cell expression vectors include xcex2-lactamase (penicillinase), lactose promoter system (Chang et al., Nature 275:615, 1978; and Goeddel et al., Nature 281:544, 1979), tryptophan (trp) promoter system (Goeddel et al., Nucl. Acids Res. 8:4057, 1980; and EP-A-36776) and tac promoter (Maniatis, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, p. 412, 1982). A particularly useful prokaryotic host cell expression system employs a phage xcex PL promoter and a cI857ts thermolabile repressor sequence. Plasmid vectors available from the American Type Culture Collection which incorporate derivatives of the xcex PL promoter include plasmid pHUB2 (resident in E. coli strain JMB9 (ATCC 37092)) and pPLc28 (resident in E. coli RR1 (ATCC 53082)).
TACE polypeptides alternatively may be expressed in yeast host cells, preferably from the Saccharomyces genus (e.g., S. cerevisiae). Other genera of yeast, such as Pichia, K. lactis or Kluyveromyces, may also be employed. Yeast vectors will often contain an origin of replication sequence from a 2xcexc yeast plasmid, an autonomously replicating sequence (ARS), a promoter region, sequences for polyadenylation, sequences for transcription termination, and a selectable marker gene. Suitable promoter sequences for yeast vectors include, among others, promoters for metallothionein, 3-phosphoglycerate kinase (Hitzeman et al., J. Biol. Chem. 255:2073, 1980) or other glycolytic enzymes (Hess et al., J. Adv. Enzyme Reg. 7:149, 1968; and Holland et al., Biochem. 17:4900, 1978), such as enolase, glyceraldehyde-3-phosphate dehydrogenase, hexokinase, pyruvate decarboxylase, phosphofructokinase, glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvate kinase, triosephosphate isomerase, phosphoglucose isomerase, and glucokinase. Other suitable vectors and promoters for use in yeast expression are further described in Hitzeman, EPA-73,657 or in Fleer et. al., Gene, 107:285-195 (1991); and van den Berg et. al., Bio/Technology, 8:135-139 (1990). Another alternative is the glucose-repressible ADH2 promoter described by Russell et al. (J. Biol. Chem. 258:2674, 1982) and Beier et al. (Nature 300:724, 1982). Shuttle vectors replicable in both yeast and E. coli may be constructed by inserting DNA sequences from pBR322 for selection and replication in E. coli (Ampr gene and origin of replication) into the above-described yeast vectors.
The yeast xcex1-factor leader sequence may be employed to direct secretion of a TACE polypeptide. The xcex1-factor leader sequence is often inserted between the promoter sequence and the structural gene sequence. See, e.g., Kurjan et al., Cell 30:933, 1982; Bitter et al., Proc. Natl. Acad. Sci. USA 81:5330, 1984; U.S. Pat. No. 4,546,082; and EP 324,274. Other leader sequences suitable for facilitating secretion of recombinant polypeptides from yeast hosts are known to those of skill in the art. A leader sequence may be modified near its 3xe2x80x2 end to contain one or more restriction sites. This will facilitate fusion of the leader sequence to the structural gene.
Yeast transformation protocols are known to those of skill in the art. One such protocol is described by Hinnen et al., Proc. Natl. Acad. Sci. USA 75:1929, 1978. The Hinnen et al. protocol selects for Trp + transformants in a selective medium, wherein the selective medium consists of 0.67% yeast nitrogen base, 0.5% casamino acids, 2% glucose, 10 xcexcg/ml adenine and 20 xcexcg/ml uracil.
Yeast host cells transformed by vectors containing ADH2 promoter sequence may be grown for inducing expression in a xe2x80x9crichxe2x80x9d medium. An example of a rich medium is one consisting of 1% yeast extract, 2% peptone, and 1% glucose supplemented with 80 xcexcg/ml adenine and 80 xcexcg/ml uracil. Derepression of the ADH2 promoter occurs when glucose is exhausted from the medium.
Mammalian or insect host cell culture systems could also be employed to express recombinant TACE polypeptides. Baculovirus systems for production of heterologous proteins in insect cells are reviewed by Luckow and Summers, Bio/Technology 6:47 (1988). Established cell lines of mammalian origin also may be employed. Examples of suitable mammalian host cell lines include the COS-7 line of monkey kidney cells (ATCC CRL 1651) (Gluzman et al., Cell 23:175, 1981), L cells, C127 cells, 3T3 cells (ATCC CCL 163), Chinese hamster ovary (CHO) cells, HeLa cells, and BHK (ATCC CRL 10) cell lines, and the CV-1/EBNA-1 cell line derived from the African green monkey kidney cell line CVI (ATCC CCL 70) as described by McMahan et al. (EMBO J. 10: 2821, 1991).
Transcriptional and translational control sequences for mammalian host cell expression vectors may be excised from viral genomes. Commonly used promoter sequences and enhancer sequences are derived from Polyoma virus, Adenovirus 2, Simian Virus 40 (SV40), and human cytomegalovirus. DNA sequences derived from the SV40 viral genome, for example, SV40 origin, early and late promoter, enhancer, splice, and polyadenylation sites may be used to provide other genetic elements for expression of a structural gene sequence in a an host cell. Viral early and late promoters are particularly useful because both are easily obtained from a viral genome as a fragment which may also contain a viral origin of replication (Fiers et al., Nature 273:113, 1978). Smaller or larger SV40 fragments may also be used, provided the approximately 250 bp sequence extending from the Hind III site toward the Bgl I site located in the SV40 viral origin of replication site is included.
Exemplary expression vectors for use in mammalian host cells can be constructed as disclosed by Okayama and Berg (Mol. Cell. Biol. 3:280, 1983). A useful system for stable high level expression of mammalian cDNAs in C127 murine mammary epithelial cells can be constructed substantially as described by Cosman et al. (Mol. Immunol. 23:935, 1986). A useful high expression vector, PMLSV N1/N4, described by Cosman et al., Nature 312:768, 1984 has been deposited as ATCC 39890. Additional useful mammalian expression vectors are described in EP-A-0367566, and in U.S. patent application Ser. No. 07/701,415, filed May 16, 1991, incorporated by reference herein. The vectors may be derived from retroviruses. In place of the native signal sequence, a heterologous signal sequence may be added, such as the signal sequence for IL-7 described in U.S. Pat. No. 4,965,195; the signal sequence for IL-2 receptor described in Cosman et al., Nature 312:768 (1984); the IL-4 signal peptide described in EP 367,566; the type I IL-1 receptor signal peptide described in U.S. Pat. No. 4,968,607; and the type II IL-1 receptor signal peptide described in EP 460,846.
An isolated and purified TACE protein according to the invention may be produced by recombinant expression systems as described above or purified from naturally occurring cells. TACE can be substantially purified, as indicated by a single protein band upon analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). One process for producing TACE comprises culturing a host cell transformed with an expression vector comprising a DNA sequence that encodes TACE under conditions sufficient to promote expression of TACE. TACE is then recovered from culture medium or cell extracts, depending upon the expression system employed. As is known to the skilled artisan, procedures for purifying a recombinant protein will vary according to such factors as the type of host cells employed and whether or not the recombinant protein is secreted into the culture medium. For example, when expression systems that secrete the recombinant protein are employed, the culture medium first may be concentrated using a commercially available protein concentration filter, for example, an Amicon or Millipore Pellicon ultrafiltration unit. Following the concentration step, the concentrate can be applied to a purification matrix such as a gel filtration medium. Alternatively, an anion exchange resin can be employed, for example, a matrix or substrate having pendant diethylarninoethyl (DEAE) groups. The matrices can be acrylamide, agarose, dextran, cellulose or other types commonly employed in protein purification. Alternatively, a cation exchange step can be employed. Suitable cation exchangers include various insoluble matrices comprising sulfopropyl or carboxymethyl groups. Sulfopropyl groups are preferred. Finally, one or more reversed-phase high performance liquid chromatography (RP-HPLC) steps employing hydrophobic RP-HPLC media, (e.g., silica gel having pendant methyl or other aliphatic groups) can be employed to further purify TACE. Some or all of the foregoing purification steps, in various combinations, are well known and can be employed to provide an isolated and purified recombinant protein.
In addition to recombinantly producing TACE, TACE may be isolated and purified from an activated monocytic cell line, THP-1. THP-1 cells typically produce more TNF-xcex1 than do HL-60 cells, and are a preferred source for TACE. Other sources for TACE may be used, and TACE may also be found in other types of cells that produce TNF-xcex1. Once a source for TACE is identified, TACE may be isolated and purified by first optionally stimulating the source cells to produce TNF-xcex1. Stimulation may not be necessary, however, it can be done using techniques that are well-known in the art. The cells are then harvested, washed, and plasma membranes isolated according to conventional procedures. A particularly preferred method of isolating the plasma membranes is method number three as described in Maeda et. al., Biochim. et. Biophys. Acta, 731:115 (1983); except that dithiothreitol should not be included in this method since it was determined that dithiothreitol blocks TACE activity. Proteins from the cell membrane then can be solubilized by suspending the membrane preparation in a dilute solution of non-ionic detergent, followed by brief homogenization. Phospholipids then can be extracted using conventional methods.
It is possible to utilize an affinity column comprising a TACE-binding protein to affinity-purify expressed TACE polypeptides. TACE polypeptides can be removed from an affinity column using conventional techniques, e.g., in a high salt elution buffer and then dialyzed into a lower salt buffer for use or by changing pH or other components depending on the affinity matrix utilized. Example 4 describes a procedure for employing TACE of the invention to generate monoclonal antibodies directed against TACE.
Recombinant protein produced in bacterial culture is usually isolated by initial disruption of the host cells, centrifugation, extraction from cell pellets if an insoluble polypeptide, or from the supernatant fluid if a soluble polypeptide, followed by one or more concentration, salting-out, ion exchange, affinity purification or size exclusion chromatography steps. Finally, RP-HPLC can be employed for final purification steps. Microbial cells can be disrupted by any convenient method, including freeze-thaw cycling, sonication, mechanical disruption, or use of cell lysing agents.
Transformed yeast host cells are preferably employed to express TACE as a secreted polypeptide in order to simplify purification. Secreted recombinant polypeptide from a yeast host cell fermentation can be purified by methods analogous to those disclosed by Urdal et al. (J. Chromatog. 296:171, 1984). Urdal et al. describe two sequential, reversed-phase HPLC steps for purification of recombinant human IL-2 on a preparative HPLC column.
Antisense or sense oligonucleotides comprising a single-stranded nucleic acid sequence (either RNA or DNA) capable of binding to a target TACE mRNA sequence (forming a duplex) or to the TACE sequence in the double-stranded DNA helix (forming a triple helix) can be made according to the invention. Antisense or sense oligonucleotides, according to the present invention, comprise a fragment of the coding region of TACE cDNA. Such a fragment generally comprises at least about 14 nucleotides, preferably from about 14 to about 30 nucleotides. The ability to create an antisense or a sense oligonucleotide, based upon a cDNA sequence for a given protein is described in, for example, Stein and Cohen, Cancer Res. 48:2659, 1988 and van der Krol et al., BioTechniques 6:958, 1988.
Binding of antisense or sense oligonucleotides to target nucleic acid sequences results in the formation of complexes that block translation (RNA) or transcription (DNA) by one of several means, including enhanced degradation of the duplexes, premature termination of transcription or translation, or by other means. The antisense oligonucleotides thus may be used to block expression of TACE proteins. Antisense or sense oligonucleotides further comprise oligo-nucleotides having modified sugar-phosphodiester backbones (or other sugar linkages, such as those described in WO91/06629) and wherein such sugar linkages are resistant to endogenous nucleases. Such oligonucleotides with resistant sugar linkages are stable in vivo (i.e., capable of resisting enzymatic degradation) but retain sequence specificity to be able to bind to target nucleotide sequences. Other examples of sense or antisense oligonucleotides include those oligonucleotides which are covalently linked to organic moieties, such as those described in WO 90/10448, and other moieties that increases affinity of the oligonucleotide for a target nucleic acid sequence, such as poly-(L-lysine). Further still, intercalating agents, such as ellipticine, and alkylating agents or metal complexes may be attached to sense or antisense oligonucleotides to modify binding specificities of the antisense or sense oliginucleotide for the target nucleotide sequence.
Antisense or sense oligonucleotides may be introduced into a cell containing the target nucleic acid sequence by any gene transfer method, including, for example, CaPO4-mediated DNA transfection, electroporation, or by using gene transfer vectors such as Epstein-Barr virus. Antisense or sense oligonucleotides are preferably introduced into a cell containing the target nucleic acid sequence by insertion of the antisense or sense oligonucleotide into a suitable retroviral vector, then contacting the cell with the retrovirus vector containing the inserted sequence, either in vivo or ex vivo. Suitable retroviral vectors include, but are not limited to, the murine retrovirus M-MuLV, N2 (a retrovirus derived from M-MuLV), or or the double copy vectors designated DCT5A, DCT5B and DCT5C (see PCT Application U.S. Pat. No. 90/02656).
Sense or antisense oligonucleotides also may be introduced into a cell containing the target nucleotide sequence by formation of a conjugate with a ligand binding molecule, as described in WO 91/04753. Suitable ligand binding molecules include, but are not limited to, cell surface receptors, growth factors, other cytokines, or other ligands that bind to cell surface receptors. Preferably, conjugation of the ligand binding molecule does not substantially interfere with the ability of the ligand binding molecule to bind to its corresponding molecule or receptor, or block entry of the sense or antisense oligonucleotide or its conjugated version into the cell.
Alternatively, a sense or an antisense oligonucleotide may be introduced into a cell containing the target nucleic acid sequence by formation of an oligonucleotide-lipid complex, as described in WO 90/10448. The sense or antisense oligonucleotide-lipid complex is preferably dissociated within the cell by an endogenous lipase.
Isolated and purified TACE or a fragment thereof, and in particular, the extracellular domain of TACE, may also be useful itself as a therapeutic agent in regulating the levels of certain cell surface proteins. In addition to TNF-xcex1, other cytoidnes as well as cytokine receptors and several adhesion proteins may be released from the cell surface by TACE or related proteases. TACE or a fragment thereof, in particular, the extracellular domain of TACE, may be administered to modulate or remove cell surface cytokines, cytokine receptors and adhesion proteins involved in tumor cell growth, inflammation, or fertilization. When used as a therapeutic agent, TACE can be formulated into pharmaceutical compositions according to known methods. TACE can be combined in admixture, either as the sole active material or with other known active materials, with pharmaceutically suitable diluents (e.g., Tris-HCl, acetate, phosphate), preservatives (e.g., Thimerosal, benzyl alcohol, parabens), emulsifiers, solubilizers, adjuvants and/or carriers. Suitable carriers and their formulations are described in Remington""s Pharmaceutical Sciences, 16th ed. 1980, Mack Publishing Co. In addition, such compositions can contain TACE complexed with polyethylene glycol (PEG), metal ions, or incorporated into polymeric compounds such as polyacetic acid, polyglycolic acid, hydrogels, etc., or incorporated into liposomes, microemulsions, micelles, unilamellar or multilamellar vesicles, erythrocyte ghosts or spheroblasts. Such compositions will influence the physical state, solubility, stability, rate of in vivo release, and rate of in vivo clearance of TACE.
TACE may be assayed using any of a variety of metalloprotease assays known in the art. In general, TACE can be assayed through the use of a peptide substrate that represents the natural cleavage site of TNF-xcex1. For example, in order to detect the cleavage of a substrate by TACE, the substrate can be tagged with a fluorescent group on one side of the cleavage site and with a fluorescence-quenching group on the opposite side of the cleavage site. Upon cleavage by TACE, quenching is eliminated thus providing a detectable signal. Alternatively, the substrate may be tagged with a colorimetric leaving group that more strongly absorbs upon cleavage. Alternatively, the substrate may have a thioester group synthesized into the cleavage site of the substrate so that upon cleavage by TACE, the thiol group remains and can be easily detected using conventional methods. A particularly preferred method of detecting TACE activity in a sample is described in Example 1, infra. Other methods of detecting TACE activity may be utilized without resorting to undue experimentation.
As further described in Example 1, infra, a quantitative assay for TACE also may be used which assay involves incubating the peptide substrate, at about 1 mM, with TACE at 37xc2x0 C. for a fixed period of time; stopping the reaction by the addition of an acid or a metal chelator; and determining the extent of cleavage by HPLC analysis.
Within an aspect of the invention, TACE, and peptides based on the amino acid sequence of TACE, may be utilized to prepare antibodies that specifically bind to TACE. A specific example of such antibody preparation is described in Example 4 herein. The term xe2x80x9cantibodiesxe2x80x9d is meant to include polyclonal antibodies, monoclonal antibodies, fragments thereof such as F(ab"")2, and Fab fragments, as well as any recombinantly produced binding partners. Antibodies are defined to be specifically binding if they bind TACE with a Ka of greater than or equal to about 107 Mxe2x88x921. Affinities of binding partners or antibodies can be readily determined using conventional techniques, for example those described by Scatchard et al., Ann. N.Y. Acad. Sci., 51:660 (1949).
Polyclonal antibodies can be readily generated from a variety of sources, for example, horses, cows, goats, sheep, dogs, chickens, rabbits, mice or rats, using procedures that are well-known in the art. In general, purified TACE, or a peptide based on the amino acid sequence of TACE that is appropriately conjugated, is administered to the host animal typically through parenteral injection. The immunogenicity of TACE may be enhanced through the use of an adjuvant, for example, Freund""s complete or incomplete adjuvant. Following booster immunizations, small samples of serum are collected and tested for reactivity to TACE or the TACE peptides. Examples of various assays useful for such determination include those described in: Antibodies: A Laboratory Manual, Harlow and Lane (eds.), Cold Spring Harbor Laboratory Press, 1988; as well as procedures such as countercurrent immuno-electrophoresis (CIEP), radio-immunoassay, radio-immunoprecipitation, enzyme-linked immuno-sorbent assays (ELISA), dot blot assays, and sandwich assays, see U.S. Pat. Nos. 4,376,110 and 4,486,530.
Monoclonal antibodies may be readily prepared using well-known procedures, see for example, the procedures described in U.S. Pat. Nos. RE 32,011, 4,902,614, 4,543,439 and 4,411,993; Monoclonal Antibodies, Hybridomas: A New Dimension in Biological Analyses, Plenum Press, Kennett, McKearn, and Bechtol (eds.), 1980. Briefly, the host animals, such as mice are injected intraperitoneally at least once, and preferably at least twice at about 3 week intervals with isolated and purified TACE or conjugated TACE peptide, optionally in the presence of adjuvant. Mouse sera are then assayed by conventional dot blot technique or antibody capture (ABC) to determine which animal is best to fuse. Approximately two to three weeks later, the mice are given an intravenous boost of TACE or conjugated TACE peptide. Mice are later sacrificed and spleen cells fused with commercially available myeloma cells, such as Ag8.653 (ATCC), following established protocols. Briefly, the myeloma cells are washed several times in media and fused to mouse spleen cells at a ratio of about thee spleen cells to one myeloma cell. The fusing agent can be any suitable agent used in the art, for example, polyethylene glycol (PEG). Fusion is plated out into plates containing media that allows for the selective growth of the fused cells. The fused cells can then be allowed to grow for approximately eight days. Supernatants from resultant hybridomas are collected and added to a plate that is first coated with goat anti-mouse Ig. Following washes, a label, such as, 125I-TACE is added to each well followed by incubation. Positive wells can be subsequently detected by autoradiography. Positive clones can be grown in bulk culture and supernatants are subsequently purified over a Protein A column (Pharmacia).
The monoclonal antibodies of the invention can be produced using alternative techniques, such as those described by Alting-Mees et al., xe2x80x9cMonoclonal Antibody Expression Libraries: A Rapid Alternative to Hybridomasxe2x80x9d, Strategies in Molecular Biology 3:1-9 (1990) which is incorporated herein by reference. Similarly, binding partners can be constructed using recombinant DNA techniques to incorporate the variable regions of a gene that encodes a specific binding antibody. Such a technique is described in Larrick et al., Biotechnology, 7:394 (1989).
Other types of xe2x80x9cantibodiesxe2x80x9d may be produced using the information provided herein in conjunction with the state of knowledge in the art. For example, humanized antibodies that are capable of specifically binding TACE are also encompassed by the invention.
Once isolated and purified, the antibodies against TACE may be used to detect the presence of TACE in a sample using established assay protocols. Further, the antibodies of the invention may be used therapeutically to bind to TACE and inhibit its activity in vivo.
The purified TACE according to the invention will facilitate the discovery of inhibitors of TACE, and thus, inhibitors of excessive TNF-xcex1-release. The use of a purified TACE polypeptide in the screening of potential inhibitors thereof is important and can virtually eliminate the possibility of interfering reactions with contaminants. Such a screening assay for detecting the TACE-inhibiting activity of a molecule would typically involve mixing the potential inhibitor molecule with an appropriate substrate, incubating TACE that is at least substantially purified with the mixture, and determining the extent of substrate cleavage as, for example, described above. While various appropriate substrates may be designed for use in the assay, preferably, a peptidyl substrate is used, and which substrate comprises the amino acid sequence Leu-Ala-Gln-Ala-Val-Arg-Ser-Ser (SEQ ID NO:5).
In addition, TACE polypeptides can also be used for structure-based design of TACE-inhibitors. Such structure-based design is also known as xe2x80x9crational drug design.xe2x80x9d The TACE polypeptides can be three-dimensionally analyzed by, for example, X-ray crystallography, nuclear magnetic resonance or homology modeling, all of which are well-known methods. The use of TACE structural information in molecular modeling software systems to assist in inhibitor design and inhibitor-TACE interaction is also encompassed by the invention. Such computer-assisted modeling and drug design may utilize information such as chemical conformational analysis, electrostatic potential of the molecules, protein folding, etc. For example, most of the design of class-specific inhibitors of metalloproteases has focused on attempts to chelate or bind the catalytic zinc atom. Synthetic inhibitors are usually designed to contain a negatively-charged moiety to which is attached a series of other groups designed to fit the specificity pockets of the particular protease. A particular method of the invention comprises analyzing the three dimensional structure of TACE for likely binding sites of substrates, synthesizing a new molecule that incorporates a predictive reactive site, and assaying the new molecule as described above.
The following Examples provide an illustration of embodiments of the invention and should not be construed to limit the scope of the invention which is set forth in the appended claims. In the following Examples, all methods described are conventional unless otherwise specified.